Process of producing o-aminoaryl mercaptans and derivatives thereof



Patented July 9, 1935 THEREOF PnooEss F PRODUClNG" O -AMINO ARYL 'MERCAPTANS TENT FFI DERIVATIVES Herbert A. Lubs, John E. Cole, and iA rth ur i, Fox, I Wilmington, Del.,' assignors to E. I. du Pont de Nemours & Company, Wilmington, Del corporation of Delaware Application September 17, 1930, SeriaLNo. 482,644 a i v .No Drawing;

aryl thiazoleshave ,beenhydrolyzed by highly" M concentrated caustic potash :or by,1alcoholic potash.; In jf'1880 AL'W. ,Hofm'ann (Ber. 13, 1227) 189-200, and 7 obtained, the; o-amino thionaph thol. They heated lphenyl amino-'benzothiazole g i with alcoholic potash to 200? and 'got o-amino /N\ //N\ thiophenoln Jacobson fused l-methyl benzothia- 10 zole s s n i with solidpotassiigm hydroxide to 200 and ob 3 tainedo-aminoathio :phenol. In Ber. 13,-q18-20 I S the same year he heated the following benzo- I thiazoles I; V i r v with potassium hydroxide and obtained o-amino T x H -01 -011 -NH2 20 q s i s 3 e r fBenzol-chlorobenzo lhydroxy 1-amii 1o benzo-'"' I "thiazole' jthiazole benzothiazole, thlazol :with' fused; caustic and obtained' thesameamino gggi h gZ g i 2 33 $2 5,3 5? thiophenol. In 1887 I-lofmann (Ber., 20, 1790) action;

heated me capt b 4 The process, when conducted with fused or alv coholio caustic potash, is uneconomical because 1 f of the large quantities of caustic potash which 3 3 must be used. Caustic soda has been tried but i r H is iunsatisfactory because," while to a limited. der gree'the hydrolysis takes place, there is such exi-I -fi and obtained f cessiveflfoaming thatthe hydrolysis is commer phenoL; :Thatthis reaction is specific to the c u a c b Moreover, t t cans; t o e n not t e y group is etic potash and causticisoda hydrolysis require est d; y H a (Ber- 20, 1802) w such high. concentration of alkali-from 50 to fused 70%'-that decomposition is prevalent with the resultant formation of undesirable by-products and decrease of yield. The reaction requires considerable time, between from four to seven 7 hours being the minimum timenece'ssary; y (g Ji N our invention has for an object the hydrolysis a 7" a of aryl thiazoles to form amino-aryl-mercaptans with solid potassiu hydroxide and. Obtained bya'process which is relatively inexpensive, eas- 4 then-amino-B p o From t reverse 11y 'controlled', and remarkably efficient. Another compou obtained in h W flobject is the elimination of roam, the undesirable m-thionaphthol. j i a decomposition of thethiazole, and elimination ofa Jacobson 78a Frankenbacher (Ber. 24s: 1404) large amount of the time heretofore necessary. heated mercapto benzothiazole in a sealed tube. F i t epdbjects will be apparent as our descrip to 190-200" withv alcoholic potassium hydroxide to n ppoc eeds V and obtained O thiophenols, y These objects are accomplished by our process (Ben. 24, 1407)! also heated mercapto n'aphthyl which, in its simplest aspect, comprises the hythiazole with alcoholic potassium hydroxide to drolysis of aryl thiazoles by means of dilute caustic a1k ali',.and preferably caustic soda solutions under elevated pressures. The reaction may be 230 pounds of 1-amino-5-ethoxy-benzothiazole were stirred up with 2000 pounds of water and 230 pounds of sodium hydroxide. This mixture was heated with stirring in a suitable closed vessel for about two hours at 160 C. and under a pres- Sum o 8 P s rs u h.- After co i g. the g amino--ethoxy thiophenol, which was formed by the reaction, was isolated as the zinc salt or as the hydrochloride. The thiophenol was also isolated in an alternative manner by the addition of chloroacetic acid to produce the corresponding thioglycollic acid, from the o-amino phenol.

Example 2 200 grams of 1-amino-5-ethoxy benzcthiazole hydro-halide (which is a mixture of the bromine and chlorine salts of the benzothiazole made, for example, by the process described in U. S. application 456,289 filed by two of the joint inventors,

Herbert A. Lubs and Arthur L. Fox) were stirred up with 1,000 cc. of caustic soda solution and h a e in a l s ess w h. stir n for wo ou a a m r u e f- 2 T e pres re developed was pounds. After cooling the 2- amino-S-ethoxy thiophenol which had been formed was isolated as the aryl thioglyc ol lic acid.

Example 3- 2 r m of m o-i-eth x zoth z e hydro-halide were stirred up. with 1,000, cc. 2.0% caustic soda solution and heated in a closed vessel with stirring for one-half hour at 160 C. The pressure developed was 80 pounds at this temper-. ature. After cooling the 2-amino-5i-ethoxy-thio-J phenol formed was isolated as the aryl thiogiycoh.

lic acid.

Example 4 Exa p 3 shows. hat hehv r s s a m torily takes places within as small; amount ofasone-half hour. Conversely, the. heating ma b ont nu fo a ons p r o o t m Such as for twenty-four hours, Without bad effects. Thus, 200 grams of l-arnino-fi-ethoxy-benzothiazole hydrohalide were stirred up with 1,000 cc.

of 20 caustic soda solution and heated in a closed vessel under a pressure of 70 pounds per square inch at a temperature of 160 C. for a period of twenty-four hours. After cooling the 2-amino- 5-ethoxy-thiophenol formed was isolated as the aryl. thioglycollic acid.

Ewm a 300 grams of I-amino 5xethoxyebenzothiazole hydrohalide were heated with stirring with 1,000 cc. of by volume caustic soda solution for two hours at 160 in a closed vessel. The pressure developed was 70 pounds. After cooling the 2- amino-S-ethoxy-thiophenol formed was isolated as the aryl thioglycollic acid.

Example 6 grams of 1-amino-5-ethoxy-benzothiazole hydrohalide were heated with stirring with 1,000 cc. of 5% caustic soda solution for two hours at 160 C. and under a pressure of pounds per square inch. After cooling the 2-amino-5-ethoxythiophenol formed was isolated as the aryl thioglycollic acid.

1 Example 7 250 grams of 1-amino-3-methyl benzothiazole were heated for four hours with 1,000 cc. 25% by volume caustic soda at 190 C. The pressure developed was 125 pounds. After cooling the 2- amino-3-methyl1thiophenol formed was isolated as the aryl thioglycollic acid.

It is to be understood that numerous modifications both as to. the nature of the reactants and condition of reaction may'be made without de-' parting from the spirit of -ourinvention illustrated by the above examples. For example, we have found that. the concentration of caustic alkali, such as the causticsoda, may be'varied within wide limits, but that care should, be taken to avoid too high a concentration which results in decomposition. In general, we prefer concentrations between 5 and-30%. We have found that the temperatures under which this hydrolysis is conducted may-var-y widely; depending upon the thiazole derivative employed as a starting material and the length of time during which the hydrolysis is conducted.

'In general, however, we prefer temperatures between 100 and 300 C. The. pressure under which the reaction is carried'out', is to a certain extent dependent upon the temperature of the reaction. Our preferred range of pressures, however, lies between five pounds per square inch (above atmospheric. pressure) and 250 pounds per square inch. While our description has been illustrated for the most part by benzothiazoles, it is to be understood that any aryl thiazole, such as the naphthothiazoles, both substituted and unsubstituted, may be employed.

Our process results in obvious economies since, although we. preferably use caustic soda, there is no foaming and resultant loss therefrom. Therelative cheapness of caustic soda as compared to, caustic potash and the fact that we employed smaller amounts of caustic result in marked economies of operation. In general, we conduct the hydrolysis with solutions which contain an amount of caustic alkali equal to the-amount of thiazole which is being hydrolyzed, The time necessary for completion of the reaction is very materially shortened by our process, resulting in a saving of not only time, itself, but labor and fuel. In general, our process results in products which are of unusual purity and-which are ob-' tained in yields varying between and of the. theoretical depending, to a certain extent, upon the conditions of operation.

Since many embodiments of this invention, differing widely in one or more respects, may be made without departing from the spirit of our invention, itis to beunderstood that we donot limit ourselves to. the foregoing examples. or description except as indicated in the followi ng claims:

' 1. A-processof producing o-amino-aryl merca'ptans which'comprises reacting an aryl amino reacting an amino-benzo-thiazole with an aqueous solution of an alkali metal hydroxide under superatmospheric pressure at a temperature above about 100 C. and below the decomposition temperature of the o-amino-aryl-mercaptan,

said aqueous solution having an alkali concentration below about 30% and containing at least three mols of alkali metal hydroxide per mol of aminobenzothiazole body.

3. A process of preparing an o-amino-arylmercaptan of the benzene series which comprises reacting an amino-benzo-thiazole with a 5 to 30% aqueous sodium hydroxide solution containing at least three mols of sodium hydroxide per molof aminobenzothiazole .at a temperature within the range above about 100 C. but below the decomposition temperature of the o-aminoaryl-mercaptan and under a superatmospheric pressure.

4. The process ofpreparing Z-amino-B-ethoxy thiophenol which comprises heating l-amino-5- ethoXy-benzothiazole hydrohalide with an aqueous caustic alkali solution under autogenous super-atmospheric pressure at a temperature of about 160 C., the amountof caustic alkali corresponding to at least three mols per mol of 1- amino-5-ethoxy-benzothiazole-hydrohalide and the concentration of the caustic alkali solution being less than about 30% caustic alkali.

5. A process or preparing 2-amino-5-ethoxythiophenol which comprises reacting 1-amino-5- ethoxy-benzothiazole hydrohalide with a caustic soda solution having a concentration below about 30% and containing at least three mols of caustic soda per mol of 1-amino-5-ethoxy-benzothiazolehydrohalide under super-atmospheric pressure at a temperature above about 100 (land below the decomposition temperature of the 2-amino-5- ethoxy-thiophenol.

6. A process of preparing 2-amino-3-methy1- thiophenol which comprises reacting 1-amino-3- methyl-benzothiazole with a caustic soda solution having a concentration below about 30% and containing at least three mols of caustic soda per mol of l-amino-3-methyl benzothiazole under super-atmospheric pressure at a temperature above about C. and below the decomposition temperature of the 2-amino-3-methyl-thiophenol. v

'7. A process of preparing 2-amino-5-ethoxythiophenol which comprises reacting 1-amino-5 ethoxy-benzothiazole hydrohalide with a caustic soda solution having a concentration of about 5% to about 30% and containing at least 3 mols of caustic soda per mol of 1-amino-5-ethoxy-benzothiazole-hydrohalide under super-atmospheric pressure at a temperature of about C.

8. In a process of producing ortho-amino-arylmercaptans, the step which comprises hydrolyzing an aryl-thiazole with an alkali metal hydroxide 'solutioncontaining water and an amo unt of alkali metal hydroxide at least equal to the amount theoretically required to break the thiazole ring and form an alkali metal salt of the mercaptan whilein the'course of the reaction having the concentration of the caustic alkali solution below about 30% caustic alkali and at the sametime operating under super-atmospheric pressure at temperatures above about 100- C.-but below temperatures giving rise to the formation of substantial amounts of decomposition products.

9. In a process of producing ortho-amino-arylmercaptans, the step which comprises hydrolyzing an aryl-thiazole with a sodium hydroxide solution containing an amount of sodium hydroxide at least equal to the amount theoretically required to break the thiazole ring and form an alkali metal salt of the mercaptan and an amount of water such that the concentration of the sodium hydroxide solution in the course of the reaction is below about 30% sodium hydroxide, while maintaining super-atmospheric pressure in the reaction zone and carrying out the reaction at a temperature about above 100 C. but below temperatures giving rise to the formation of substantial amounts of decomposition products.

10. In a process of producing ortho-aminoaryl-mercaptans, the step which comprises hydrolyzing an aryl-amino-thiazole with a watercontaining solution of an alkali metal hydroxide having a concentration below about 30% and containing at least three mols of alkali metal hydroxide per mol of aryl-amino-thiazole under super-atmospheric pressure at a temperature above 100 C. but below temperatures giving rise to the formation of substantial amounts of containing at least three mols of caustic soda per mol of aryl-amino-thiazole under a super-atmospheric pressure below 250 pounds per square inchat atemperature above 100" C. but below temperatures giving rise to the formation of substantial amounts of decomposition products.

'12. In a process of producing ortho-aminoaryl-mercaptans, the step. which comprises hydrolyzing an arylamino-thiazole with an alkali metal hydroxide solution containing an amount of alkali metal hydroxide approximately equal on a weight basis to the amount of thiazole body and an amount of water such that the concentration of the alkali metal hydroxide solution in the course of the reaction is below about 30% alkali metal hydroxide, while maintaining superatmospheric pressure in the reaction zone and carrying out the reaction at a temperature above about 100? C. but below temperatures giving rise to the formation of substantial amounts of decomposition products. 7

13. In a process of producing ortho-aminoalkyl substituted phenyl mercaptans, the step which comprises hydrolyzing an aminobenzothiazole containing an alkyl substituent in its benzene nucleus with an alkali metal hydroxide solution containing at least three mols of alkali metal hydroxide per mol of thiazole body and an amount of water such that the concentration of the alkali metal hydroxide solution in the course of the reaction is below about 30% alkali metal hydroxide, while maintaining super-at- 10 metal hydroxide per mol of thiazole body and an amount of *water such that the oonomtmflon of the alkali metal hydroxide solution in the course of the reaction is below about 30% alkali metal hydroxide, while maintaining super-atmosphenic pressure in the reaction Bone and can'ying out the react-ion at a temperature of about 160 C.

HERBERT A. LUBS. JOHN EL COLE. ARTHUR. L. FOX. 

